(1) Field of the Invention
This invention relates to improvements in a resin panel in which a skin layer is formed on its surface and an expanded layer having a multiplicity of voids are formed inside it and improvements in a method for manufacturing the resin panel.
(2) Description of the Related Art
Registered Japanese Utility-Model Publication No. 2538513 (hereinafter, referred to as Patent Document 1) discloses a technique of forming a resin panel having hollows inside it by blow molding and thereby saving its weight. In the case of this resin panel, the opposed panel surfaces are deformed to form cylindrical support parts therebetween by pressing a parison from both sides with halves of a mold assembly in blow molding and, after the removal of the resin panel from the mold assembly, metal pipes are pressed in the support parts, respectively, to provide rigidity.
In the resin panel disclosed in Patent Document 1, however, the contours of the support parts for supporting the metal pipes pressed in them are exposed as recesses at the external surface of the resin panel, which disfigures the appearance of the resin panel. Further, since the panel inside is formed not of an expanded layer having a multiplicity of voids but of hollows, deformations such as warpages occur on the surfaces, which further deteriorates the resin panel appearance. Furthermore, since the press-in of the metal pipes are carried out after blow molding, a loose press-in would cause the metal pipe to drop out of or rattle against the cylindrical support part. If the resin panel in this state is applied to a motor vehicle, vibration sounds might be produced. In order to eliminate these drawbacks, the resin panel must be molded with high precision. This increases the number of manufacturing steps.